This invention relates to a system for encoding a complex optical image onto a coherent laser beam and for utilizing the information encoded in an optical correlator system.
More particularly, this invention relates to a system utilizing one or more liquid crystal television receivers for encoding amplitude and phase components of a complex image onto a coherent laser beam.
It is known to use modified liquid crystal television receivers as a spatial light modulator, as shown in U.S. Pat. No. 4,715,683. This patent describes a VanderLugt architecture correlator using a liquid crystal television receiver as the input spatial light modulator and a holographic film plate as the matched spatial filter. The liquid crystal television receiver is used to encode the input scene onto the laser beam. This encoding is accomplished by selectively blocking portions of the beam so that the image is encoded in amplitude only. A view of an amplitude image encoded in laser light is shown in FIG. 4 of the drawings of this patent. The liquid crystal television receiver, combined with the external polarizers described in this patent blocks the light in the dark regions and passes the light in the bright regions.
Light, however, is a plurality of waves and each has both amplitude and phase. Consider the two waves in FIG. 17 of the appended drawings. The term "amplitude" refers to the height of the crests in the wave. The term "phase" refers to the alignment between the crests in one wave and the crests in the other wave. The eye, film, and video cameras all see intensity, which is a function of the amplitude of the light wave. The liquid crystal television receiver can also modulate phase. This phase modulation can be thought of as a delay in the waves. Suppose the crests of two waves were initially aligned as in FIG. 18. These two waves now pass through different portions, or pixels, of the liquid crystal television receiver. An image can be encoded on the light waves by selectively delaying one wave with respect to the other. If one pixel is "on" and the other pixel is "off", one of the waves will be delayed with respect to the other as shown in FIG. 19. The crests of the light wave are no longer aligned. Most sensors such as the eye cannot see this type of encoding but it can be used in the optical correlators of the invention. This type of encoding is more light efficient because no light is thrown away as in the amplitude only encoding of U.S. Pat. No. 4,715,683. Prior to the invention of the applicants', no one had thought of using the phase modulation property of the liquid crystal television receiver in this manner.
In the past, the liquid crystal television receivers have been useful only after the user has removed low quality polarizers glued to the liquid crystal television receiver and replaced them with high quality external polarizers. The use of such high quality external polarizers results in high costs in both money and light efficiency and has made the use of these polarizers undesirable.